This invention relates to a method of producing a semiconductor displacement transducer in which a semiconductor strain detector is bonded to a metal strain generator by means of a metal junction layer.
The semiconductor displacement transducer usually utilizes the mechano-electrical conversion effect in a semiconductor which is usually the piezo-resistance effect in principle. It is a well-known fact that a semiconductor strain detector using the piezo-resistance effect has an output sensitivity several tens of times higher than that of the conventional strain detector using a metal strain gauge.
In this type of semiconductor strain detectors, a strain-sensitive region is formed by diffusing an impurity into a portion of the main surface of a semiconductor single crystal substrate. Since the semiconductor single crystal substrate is an excellent elastic strain generator, the substrate itself is often used as an elastic strain generator in the structure of a semiconductor displacement transducer. However, this constitution is limited only to the case where strain to be generated is relatively small since the semiconductor single crystal substrate is brittle. Accordingly, in order to realize a semiconductor displacement transducer serviceable in relatively large strain conditions, a semiconductor strain detector must be bonded in metal junction to a metal strain generator by means of an insulating oxide film, as disclosed in, for example, U.S. Pat. No. 4,151,502, issued to Y. Kurihara et al on Apr. 24, 1979, entitled "Semiconductor Transducer".
Such semiconductor displacement transducers are usually used in a wide range of temperatures, i.e. from -40.degree. C. to 120.degree. C., and therefore the metal junction layer undergoes creep due to repeated generation of strain especially at high temperatures. As a result, a zero point drift occurred in the output so that a stable characteristic cannot be obtained.